The present invention relates to an apparatus and a method for controlling knocking in an internal combustion engine such as an automotive gasoline engine which detects knock in the engine and controls various engine control parameters in a direction to suppress the knocking. More particularly, it relates to such a knock control apparatus and method which is able to improve knock control and reduce the cost of manufacture thereof.
In general, in an internal combustion engine such as an automotive gasoline engine having a plurality of cylinders, the air/fuel mixture in each cylinder is compressed and fired at an optimum ignition point so as to produce maximum output power without incurring knocking. To properly control the operations of the respective cylinders, it is common practice to employ a microcomputer which controls the ignition timing, the fuel injection order, the fuel injection timing and the like for the respective cylinders in an optimal manner.
Among engine control parameters such as the amount of fuel injected into each cylinder, ignition timing, etc., if ignition timing is controlled to be excessively advanced for example, engine vibrations called knocking are caused by abnormal combustion of the air/fuel mixture in a cylinder, and the cylinder may be damaged or destructed. In order to avoid such a situation, when abnormal engine vibrations are detected by a sensor, engine control parameters should be controlled in a sense to suppress knocking. For example, the ignition timing for the cylinder that is knocking is retarded or the amount of fuel to be injected into the knocking cylinder is decreased.
FIG. 7 shows a block diagram of a conventional knock control apparatus for an internal combustion engine. In this figure, the apparatus illustrated comprises a knock sensor 1 in the form of an acceleration sensor and the like installed on an engine for sensing knocking in the engine, e.g., for sensing vibrational accelerations of the cylinders due to knocking and generating a corresponding electrical output signal A, a knock detecting circuit 2 for identifying signals due to the knocking in the output signal of the knock sensor 1 and generating an output signal V.sub.R in an analog form when knocking is detected, an analog to digital (A/D) converter 3 for converting the analog output signal of the knock detecting circuit 2 into a digital signal, and an engine control unit 4 (hereinafter referred to as an ECU) in the form of a microcomputer including an ignition timing controller 5 connected to receive the digital signal from the A/D converter 3 for controlling the ignition timing of the engine in an appropriate manner so as to suppress knocking in the engine. The knock detecting circuit 2 includes a band-pass filter 22 for filtering a particular frequency band of the output signal A of the knock sensor 1, a gate circuit 23 operable, through the action of a mask signal M from the ECU 4, to pass specific portions of the output signal of the band-pass filter 22, a BGL circuit 24 connected to receive the output signal of the gate circuit 23 for generating an output signal A' of a background level, a comparator 25 having a first input terminal connected to receive the output signal A' of the gate circuit 23 and a second input terminal which is supplied with the output signal of the BGL circuit 24 for making a comparison between these input signals, and an integrator 26 having an input terminal coupled to the output terminal of the comparator 25 and an output terminal coupled to the input terminal of the A/D converter 3 for integrating the output signal of the comparator 25 and outputting an analog signal to the A/D converter 3, the integrator 26 further having a reset terminal coupled to the ECU 4 such that it is reset by a reset signal R from the ECU 4.
FIG. 8 shows in diagrammatic form the waveforms of the output signal A of the knock sensor 1, the mask signal M, the gate circuit output signal A', the BGL signal and the integrator output signal V.sub.R, respectively, of the knock control apparatus of FIG. 7.
The conventional knock control apparatus as constructed above operates as follows. First, the knock sensor 1 generates an output signal which is input to the band-pass filter 22 where a specific frequency band thereof is filtered and passed to the gate circuit 23. The gate circuit 23, which has a gate control terminal supplied from the ECU 4 with a mask signal R containing square pulses occurring at predetermined intervals, operates to mask the output signal of the knock sensor 1 as filtered through the band-pass filter 2 in such a manner that those portions of the knock sensor output signal A which correspond to the respective square pulses of the mask signal M are removed to provide an output signal which contains no pulse at locations corresponding to the respective square pulses of the mask signal M. The output signal of the gate circuit 23 is input to the first input terminal of the comparator 25, and at the same time it is imposed on the input terminal of the BGL circuit 24 so that the BGL circuit 24 produces an output signal having a predetermined background voltage level. The background level voltage of the BGL circuit 24 is imposed on the second input terminal of the comparator 25 and compared with the output signal of the gate circuit 23 fed to the first input terminal of the comparator 25, so that the comparator 25 generates an output signal when the output signal of the gate circuit 23 is higher than the background voltage level. The output signal of the comparator 25 is fed to the integrator 26 which performs integration to generate an output signal, as shown in FIG. 8. In this regard, it is to be noted that although not illustrated in FIG. 7, in case of a multi-cylinder internal combustion engine, a plurality of knock sensors 1 are employed one for each engine cylinder, and the output signals of the respective knock sensors 1 are fed to the integrator 26 in a parallel relation with each other through the band-pass filter 22, the gate circuit 23 and the comparator 25 so that they are respectively integrated by the integrator 26 to provide corresponding output signals. To this end, the ECU 4 feeds a reset signal for each knock sensor output to the reset terminal of the integrator 26 at an appropriate timing. The integrated output signal of the analog form of the integrator 26 is then fed to the A/D converter 3 and converted there into a digital signal V.sub.R which, in turn, is read into the ECU 4 where, based on the digital signal V.sub.R, the ignition timing controller 5 successively calculates an appropriate knock-suppression retard angle .sub.R using the following formula; EQU .theta..sub.R =.theta..sub.R *+.DELTA..theta..sub.R ( 1)
where .theta..sub.R * is the last knock-suppression retard angle, and .DELTA..theta..sub.R is expressed as follows: EQU .DELTA..theta..sub.R =V.sub.R .times.L
where L is a modification coefficient.
With the above-mentioned conventional knock control apparatus, however, the knock detecting circuit 2, which is a hardware component, includes a knock determining means comprising the BGL circuit 24, the comparator 25 and the integrator 26 for determining whether or not there is knocking in the engine. Such a knock determining processing requires a rather complicated circuit arrangement and besides puts a tremendous load on the controlling hardware, resulting in high manufacturing costs.